After reading some reviews I've bought the tiny 35mm together with my A7r. Most reviewers say something like "not as good as the 55mm, but a decent performer". Maybe I have a different opinion about the meaning of decent, but after using it for a while I've got a different conclusion about the lens. I see massive vignetting and not so sharp corners.
For example, I compared it to the Nikkor 24-70 zoom lens. At the price of 790€, it should be able to beat the zoom, shouldn't it? Look for yourself:
Unfortunately, I have no other well-performing 35mm lens to compare. So I took a look at photozone.de. They tested the lens and it got 3.5 of 5 possible stars.
I know it is problematic to compare MTF results across different camera systems, but I think it is safe to say that the same lens delivers higher numbers when mounted on a higher megapixel body. In reverse you can say that a different lens that produces the same numbers on a lower MP body is optically better. So lets take a look what the Sigma 35 1.4 delivers on a 24MP D3x, at F5.6:
The Sony FE 35 in comparison, at F5.6. On a camera body with 36MP:
Another lens, the Carl Zeiss Distagon 35mm F2.0, also on a 24MP Nikon D3x:
All numbers by photozone.de.
I think it is safe to say that both lenses would massively outperform the FE35, when mounted on a 36MP body.
The real problem of the lens is the price. For 790€ (more than the Sigma!) I really expected a lot more. If Sony had priced it at 399€ I wouldn't have written any negative word about it.
On the other hand this is just pixel-peeping
A recent snapshot with the FE35: